According to research by Finnish Environment Institute SYKE and University of Eastern Finland, microplastics are now found in all Baltic waters and in fish, bivalve molluscs and benthic fauna.
Microplastics were found in all of the studied groups of organisms. The largest number of microplastics were found in blue mussels that filter water in order to feed. Fewer quantities were found in the most common benthic fauna, that is, Baltic clam, Marenzelleria polychaetes and chironomid larvae.
Microplastics most likely end up in aquatic organisms when they feed. Exposure is affected by the habitat, prey and feeding method.
Microplastics cause stress to the aquatic organisms and may expose them to harmful substances. These were the results of a recently completed project that studied the behaviour of microscopic plastic pollution in water systems and developed research methods focusing on microplastics.
Major differences were found in the quantities of microplastics in fish, both regionally and among fish species. In the study, only a very small quantity of plastics was found in Baltic herring, Baltic sprat and three-spined stickleback in the open sea.
Microplastics were noticeably more frequent or abundant in European perch, common bleak and three-spined stickleback on the Finnish coast as well as in European perch and vendace in Lake Kallavesi. The method developed over the course of the project improved the accuracy of analysis, enabling the identification of smaller particles than before.
Microplastics are found everywhere
‘Field studies indicate that microplastics are found everywhere, that is, in the surface layers of water, deeper in the water column, on the sea bed and in fish, bivalve molluscs and benthic fauna. The smaller microplastics we study, the higher concentrations we observe. This is because plastics constantly fragment into smaller particles in the environment,’ explained Maiju Lehtiniemi, Research Professor at the Finnish Environment Institute.
In surface waters, microplastics were found similar concentrations both in Finland’s coastal waters and in Lake Kallavesi close to the city of Kuopio. This is probably due to the fact that the sources of microplastics ending up in water systems are mostly located on land. In the Baltic Sea, stratification seems to affect the concentrations of microplastics in the different layers of water.
The sediment at the bottom of the Baltic Sea contains higher concentrations of microplastics than the water in the area. Relatively high local concentrations of microplastic particles were observed in coastal sediments. The quantities reach the same levels as in Norway’s coastal sediments and in the southern Baltic Sea, for example.
‘Microplastics end up in water systems from land especially via flowing waters. One of the most important pathways is storm water, that is, rain and melt water from built-up areas. Research results indicate that storm water in urban environments contains microplastics and that the temporal and local variation in the quantity of microplastics is significant. In the future, more research is required particularly on microplastics emissions from transport,’ said Julia Talvitie, Researcher at the Finnish Environment Institute.
Microplastics cause stress to aquatic organisms
Laboratory tests indicated that plastic and recycled rubber causes stress in plankton and Baltic clam. Small planktonic crustaceans died or had higher stress levels when exposed to rubber used in car tyres and frozen vegetable bags (light PE) containing food residues. Harmful substances, such as metals and PAHs, were observed in Baltic clam exposed to car tyre rubber.
Spectroscopic analysis methods for examining the plastic types of particles found in environmental samples were developed in the project.
‘The most common types of plastic found in the samples were the same in both the Baltic Sea and Lake Kallavesi as well as in fish and benthic fauna,’ said Arto Koistinen, Director of SIB Labs and the University of Eastern Finland’s sub-project. Polyethylene (PE) was often the most abundant type of plastic in the samples. This is understandable as the various forms of polyethylene are the world’s most used raw materials of plastic. Polypropylene (PP) was also found in all samples examined. Another type of plastic commonly found in the samples was polyethylene terephthalate (PET). PP and PET are plastics widely used in consumer products, including packaging.
In environmental samples, fibres were more common than particles. Because plastic fibres and particles are found everywhere in our living environment, sampling and laboratory work require special care and quality assurance to ensure the reliability of results.
Over the course of the project, the methods of microplastics research have improved significantly both in Finland and internationally, and the information on microplastic concentrations and microplastic materials has become considerably more accurate. The project has played an important role in gathering and sharing information on microplastics.